Method of regulating an electric motor and corresponding electric motor

ABSTRACT

A method of regulating an electric motor, regulation being implemented with a loop of gain less than unity as a function of a divergence between a setpoint signal for an operating parameter of the motor and a measured value of the same operating parameter of the electric motor, the divergence being taken into account only if said divergence is greater than a predetermined threshold whenever the measured value is greater than the setpoint signal.

[0001] The present invention relates to a method of regulating anelectric motor suitable for use, for example, in a motor vehicle fanunit for driving a cooling fan for the internal combustion engine of avehicle.

[0002] It is known for such electric motors to be controlled as afunction of a temperature measured on the internal combustion engine,preferably in association with regulation of the real speed of theelectric motor as measured by means of suitable sensors, such as Halleffect sensors.

[0003] In known methods, regulation is generally performed using acontrol loop operating on a difference between a setpoint signalrepresentative of an operating parameter of the electric motor and ameasured value of said parameter. The reaction speed of the regulationloop depends on its gain which is generally less than unity.Unfortunately, the setpoint value for a fan unit can vary frequently, inparticular in stop-go traffic in which the driver alternates betweenaccelerating and slowing down. Existing systems are then not verysatisfactory for regulating the speed of the fan unit.

[0004] In a regulation loop that possesses low gain, the time needed forreaching the value desired for the operating parameter is too longcompared with the frequency at which the setpoint is changed, such thatthe fan unit does not reach the setpoint before the setpoint changes.

[0005] Conversely, in a regulation loop that possesses high gain, thefan unit reaches the setpoint, passing in alternation through valuesthat are less than and greater than the setpoint with sudden changes ofspeed that are particularly noisy and that are perceived by the user ofthe vehicle and are detrimental to user comfort.

[0006] The invention seeks to propose a method enabling regulation to beperformed sufficiently quickly, while nevertheless limiting the risk ofinstability in the speed of the electric motor.

[0007] The invention provides a method of regulating an electric motor,regulation being implemented using a loop of gain less than unity, as afunction of a divergence calculated on the basis of a difference betweena setpoint signal representative of an operating parameter of the motorand a measured value of the same operating parameter, the divergencebeing taken into account when the measured value is greater than thesetpoint signal only if the divergence is greater than a predeterminedthreshold.

[0008] Thus, when the speed of the fan unit exceeds the setpoint valueby a divergence that is less than the threshold, the regulation loopceases to be effective. The number of changes of speed is thus minimizedand vehicle user comfort is improved.

[0009] Advantageously, the gain is equal to one-fourth, and thepredetermined threshold is equal to 2% of the setpoint signal.

[0010] This provides an optimum compromise between the speed at whichthe operating parameter adapts to the setpoint and stability of electricmotor speed.

[0011] Furthermore, the cost of Hall effect sensors is relatively high.The use of Hall effect sensors thus constitutes a major drawback in thefield of motor equipment where questions of unit cost price are of majorimportance because of the increasing amount of equipment that needs tobe installed on a vehicle in order to improve user comfort.

[0012] In a particular embodiment, the setpoint is a pulse voltagesetpoint having a duty ratio representative of a percentage of a nominalspeed of rotation of the electric motor, the setpoint being converted tocorrespond to a mean voltage prior to calculating the divergence betweenthe setpoint and the measured value.

[0013] The Hall effect sensors are thus replaced by a voltage sensorwhich is less expensive.

[0014] Also preferably, the method includes steps of measuring currentat the terminals of the electric motor and of feeding the electric motorin such a manner as to maintain the measured current at a value that isless than or equal to a predetermined current threshold.

[0015] This makes it possible to limit the torque delivered by the motorwhen a relatively large opposing torque is applied to the outlet shaftthereof, in particular during starting or in the event of the fan beingblocked, accidentally. The risk of damaging the electric motor byoverloading it is thus minimized.

[0016] The invention also provides an electric motor associated with aregulation loop of gain less than unity and with means for implementinga method presenting one of the above characteristics.

[0017] Other characteristics and advantages of the invention appear onreading the following description of a particular and non-limitingembodiment of the invention.

[0018] Reference is made to the sole accompanying FIGURE which is ablock diagram of the control system for an electric motor.

[0019] The invention is described herein in the context of anapplication to cooling the heat engine (not shown) of a motor vehicle.

[0020] The method of regulation is used for controlling an electricmotor 1 for rotating a fan (not shown) for blowing a stream of air tocool the engine.

[0021] The electric motor 1 is controlled in this circuit by means of amicroprocessor on the basis of a setpoint established as a function ofthe temperature of the engine. The temperature of the engine is eithermeasured or else determined in predictive manner, e.g. by taking accountof other operating parameters of the engine such as vehicle speed,engine speed, . . . . The setpoint is preferably delivered in the formof a pulse signal X of the pulse width modulated (PWM) type, presentinga predetermined ratio of pulse duration over period duration so as tocorrespond to a percentage of the nominal speed of rotation of theelectric motor 1.

[0022] The setpoint signal X is injected into a regulation loopcomprising a module 3 (outlined by a chain-dotted box) for digitallycorrecting the setpoint signal as a function of the difference betweenthe setpoint signal and the voltage measured by a voltage sensor 4across the terminals of the electric motor 1 in order to generate acontrol signal which is applied to the motor power supply circuit, e.g.by means of a chopper 5 which determines the width of the voltage pulsesfed to the motor.

[0023] For correction purposes, the setpoint signal X is initiallyconverted by a correction module 7 using coefficients so as to put thesignal into the form aX+b corresponding to a mean power supply voltagesetpoint. These coefficients are determined in such a manner that whenthe setpoint represents a ratio of 16%, the voltage setpoint correspondsto the minimum voltage enabling the electric motor 1 to be driven, i.e.in general, a voltage of 4 volts (V), and when the setpoint signal has aratio of 80%, the setpoint corresponds to the nominal voltage of theelectric motor, i.e. 12 V or 13.5 V depending on the type of vehicle.

[0024] The difference between the measured voltage 4 and the voltagesetpoint derived from conversion of the setpoint signal is then dividedby four (8) in order to obtain the divergence that is used forcorrecting the control signal. The gain of the regulation loop is thusequal to 0.25. In the example shown which includes a digital correctionmodule, division by four is performed very simply by shifting.

[0025] When the measured voltage is less than the calculated meanvoltage, the divergence is added to the setpoint in order to determinehow the power supply voltage is to be controlled.

[0026] When the measured voltage is greater than the calculated meanvoltage (9), the divergence is compared with the setpoint 10. If thedivergence is less than 2% of the setpoint, then the control signal isidentical to the setpoint (11). If the divergence is more than 2% of thesetpoint, then the control signal is generated by reducing the setpointby the value of the divergence (12).

[0027] Whatever the control signal that is generated, the motor currentas measured by a sensor 6 is compared with the applied control signal12. When the measured current is greater than the control signal, thecontrol signal is corrected (14) in order to bring the current to avalue that is below a limit threshold. When the control signal isapplied by means of a chopper, the current measurement is the pulsepercentage of the motor current control signal, multiplied bymeasurement gain. This gain enables the limit threshold to bedetermined.

[0028] Naturally, the invention is not limited to the embodimentdescribed and variant embodiments can be applied thereto without goingbeyond the ambit of the invention as defined by the claims.

[0029] In particular, the setpoint signal may correspond to an operatingparameter of the electric motor other than voltage, for example speed ofrotation, even though present-day speed sensors are more expensive thanvoltage sensors, as emphasized above.

[0030] Although the invention is described with reference to a systemthat has a digital correction module, it can also be implemented with ananalog system.

[0031] In addition, numerical values are given merely by way of exampleand can be modified, in particular as a function of the characteristicsof the electric motor and/or of the system with which it is associated.

1. A method of regulating an electric motor (1), regulation beingimplemented using a loop of gain less than unity, as a function of adivergence calculated on the basis of a difference between a setpointthreshold representative of an operating parameter of the motor and ameasured value for the same operating parameter of the electric motor,wherein when the measured value is greater than the setpoint signal, thedivergence is taken into account only when the divergence is greaterthan a predetermined threshold.
 2. A method according to claim 1,wherein the gain is equal to 0.25 and the predetermined threshold isequal to 2% of the signal.
 3. A method according to claim 1, wherein thesetpoint signal is a pulse voltage setpoint having a duty ratiorepresentative of a percentage of a nominal speed of rotation of theelectric motor (1), and in that the setpoint signal is converted so asto correspond to a mean voltage prior to calculating the divergencebetween the setpoint signal and the measured value.
 4. A methodaccording to claim 1, further comprising measuring a current of theelectric motor (1); and powering the electric motor in such a manner asto maintain the motor current at a value that is less than or equal to apredetermined current threshold.
 5. (Cancelled)
 6. A vehicle system,comprising: an electric motor; and a control circuit, the controlcircuit configured to regulate the electric motor using a loop of gainless than unity, as a function of a divergence calculated on a basis ofa difference between a setpoint threshold representative of an operatingparameter of the motor and a measured value for the operating parameter,the control circuit further configured to take the divergence intoaccount, when the measured value is greater than the setpoint signal,only when the divergence is greater than a predetermined threshold.
 7. Asystem according to claim 6, wherein the gain is equal to about 0.25 andthe predetermined threshold is equal to about 2% of the signal.
 8. Asystem according to claim 6, wherein the setpoint signal is a pulsevoltage setpoint having a duty ratio representative of a percentage of anominal speed of rotation of the electric motor (1), and in that thesetpoint signal is converted so as to correspond to a mean voltage priorto calculating the divergence between the setpoint signal and themeasured value.
 9. A system according to claim 6, wherein the controlcircuit is further configured to measure the current of the electricmotor (1) and power the electric motor in such a manner as to maintainthe motor current at a value that is less than or equal to apredetermined current threshold.
 10. The system of claim 6, wherein thecontrol circuit comprises a microprocessor.
 11. The system of claim 6,wherein the control circuit comprises analog circuitry.
 12. A method forcontrolling an electric motor, comprising: controlling the motor basedon an amount of deviation from a first criterion; wherein, in instanceswhere there is deviation from the first criterion, the motor will not becontrolled based on the amount of deviation from the first criterion ifa second criterion is met.
 13. The method of claim 12, wherein the firstcriterion comprises a setpoint for a parameter; and deviation from thefirst criterion is determined based on a measured value for theparameter.
 14. The method of claim 12, wherein the second criterioncomprises that the amount of deviation is within a threshold.
 15. Themethod of claim 14, wherein the first criterion comprises a setpoint;deviation from the first criterion is determined based on a measuredvalue for the parameter; and the second criterion further comprises thatthe measured value is greater than the setpoint.
 16. The method of claim12, wherein the motor is configured to control a motor vehicle function.17. The method of claim 12, wherein the motor is coupled to a fanconfigured to cool a vehicle's engine.
 18. The method of claim 12,wherein the first criterion is configured to vary based on a measuredparameter.
 19. The method of claim 18, wherein the measured parametercomprises a parameter related to a motor vehicle engine.
 20. The methodof claim 18, wherein the measured parameter comprises enginetemperature.
 21. The method of claim 12, wherein deviation from thefirst criterion is determined based on a measured value for an operatingparameter; and the operating parameter comprises a voltage supplied tothe motor.
 22. The method of claim 12, further comprising measuring acurrent of the electric motor (1); and powering the electric motor insuch a manner as to maintain the motor current at a value that is lessthan or equal to a predetermined current threshold.
 23. The method ofclaim 12, wherein the amount of deviation is measured based on a valueof a measured parameter and a value of a setpoint for the measuredparameter; and the motor is always controlled based on the amount ofdeviation if the value of the measured parameter is less than thesetpoint.
 24. A vehicle system, comprising: an electric motor; and acontrol circuit configured to control the electric motor, the controlcircuit configured to control the electric motor based on an amount ofdeviation from a first criterion, but not if a second criterion is met.25. The system of claim 24, further comprising a voltage sensor coupledto the electric motor and the control circuit, wherein the controlcircuit is configured to determine the amount of deviation based on aninput from the voltage sensor.
 26. The system of claim 24, wherein theamount of deviation is measured based on a value of a measured parameterand a value of a setpoint for the measured parameter; and the motor isalways controlled based on the amount of deviation if the value of themeasured parameter is less than the setpoint.
 27. The system of claim24, wherein the control circuit is configured to receive an inputrepresentative of a current of the electric motor and to power theelectric motor in such a manner as to maintain the motor current at avalue that is less than or equal to a predetermined current threshold.28. The system of claim 24, wherein the electric motor is coupled to afan that is configured to cool an engine of the vehicle.
 29. The systemof claim 24, wherein the first criterion varies based on a measuredparameter.
 30. The system of claim 29, wherein the measured parametercomprises a parameter related to a motor vehicle engine.
 31. The systemof claim 29, wherein the measured parameter comprises enginetemperature.
 32. A vehicle system, comprising: a motor; and a means forcontrolling the motor such that divergence from a criterion is takeninto account only when the divergence is greater than a predeterminedamount.
 33. The system of claim 32, further comprising a means forsetting the criterion.
 34. A vehicle system including an electric motor,the system comprising: a voltage sensor configured to provide a signalrepresentative of an operating voltage of the electric motor; and acontrol circuit configured to regulate the electric motor; wherein thecontrol circuit is configured to establish a setpoint for the operatingvoltage of the electric motor, to determine an amount of divergencebetween a value obtained from the signal received from the voltagesensor and the setpoint, and to regulate the electric motor based on theamount of divergence.
 35. The system of claim 34, wherein the controlcircuit will only use the amount of divergence to adjust the electricmotor if the value is one of greater than the setpoint by a thresholdamount and less than the setpoint.
 36. The system of claim 34, furthercomprising a means for determining the setpoint.